There are known oxygenators constructed to perform gas exchange by use of a multiplicity of hollow fiber membranes. An example of such an oxygenator is described in U.S. Pat. No. 6,503,451.
This oxygenator includes a housing, a hollow fiber membrane bundle received in the housing, blood-inlet and blood-outlet ports, and gas-inlet and gas-outlet ports so that gas exchange (i.e., oxygenation and carbon dioxide removal) is performed between blood and gas through the hollow fiber membranes.
In oxygenators constructed in this manner, bubbles may exist in the blood introduced through the blood inlet port. In such a case, bubbles are preferably removed by the hollow fiber membrane bundle.
However, the hollow fiber membrane bundle is specifically designed to efficiently carry out gas exchange, without being specifically intended to remove bubbles. Thus, there is a problem that bubbles are not fully removed by the hollow fiber membrane bundle, with the result that bubbles remaining in the blood that is discharged from the blood outlet port being carried downstream of the oxygenator. For this reason, a bubble-removing arterial filter is sometimes provided on an arterial line between the oxygenator and the patient.